1. Field of Invention
This invention relates to damping systems. The invention also relates to damping systems that measure the velocity of a moving part and determine an amount of damping to be applied to the moving part based on the velocity measured. The invention is more particularly related to a damping system that measures the velocity of a moving part, determines a damping factor based on the velocity, and electronically applies the damping factor to the moving part. The invention is still further related to a damping system for an actuator in a tape drive system that electronically measures actuator velocity, determines an amount of damping based on the velocity measured, and applies the damping electronically to the actuator.
2. Description of Related Art
One of the increasing demands placed on the design and manufacture of media storage devices is the ability to increase data density and thereby increase an amount of data that can be stored on the device. One method to increase data density on a tape is to increase the number of data tracks on the tape. However, increasing the number of tracks on a tape requires an increased tracking bandwidth in order to accurately place and maintain a read/write head at a selected track on the tape.
Conventional disk and tape drive systems utilize moving head systems that place the read/write head at selected tracks for reading and/or recording on a media. One type of moving head system commonly utilized in disk drive systems is a linear bearing system. FIG. 1 illustrates a conventional linear bearing system that comprises a head 10 and carriage 14 that slides along a linear bearing and rail system 12 in order to position the head 10 over an appropriate portion of a media 18 (tape) for reading and recording of data. An actuator 16 is electronically activated to apply motion required for positioning of the head 10.
The linear bearing system is an advantageous configuration because the sliding mechanism (linear bearing and rail combination), as a free-floating system, utilizes very little energy for movement and is not particularly susceptible to mechanical resonances. However, linear bearing systems will have difficulties or inaccuracies in tracking if dirt or dust particles become deposited on the rail, and therefore operate best in clean or sealed environments. Therefore, linear bearing systems are not well suited for use in tape drives because the bearing and rails are subject to dirt particle depositions from a number of sources, including particles from various tape cartridges placed in the tape drive, and particles in the air of the environment in which the tape drive is placed because the head and drive mechanisms are in an open system (i.e., not operating in a clean room or sealed in a clean environment).
FIG. 2 illustrates a conventional moving head system (spring mass system) 20 utilized in a tape drive. The moving head 10 is attached to a spring 22, and an actuator 24. The actuator 24 is electronically positioned by a voice coil 26. Thus, the voice coil 26 moves the actuator 24 to position the moving head 10 to a specific track on a tape (media 18).
The conventional tape drive moving head system is advantageous over linear bearing systems because it is less susceptible to tracking inaccuracies caused by dust particles or other dirt that may interfere with moving parts. However, because the moving head system 20 is not a free-floating system (i.e., a spring is attached to the moving head), the actuator 24 requires power to work against the spring 22 at all times. The spring also causes additional problems by increasing susceptibility of the system to mechanical resonances (the spring will resonate similar to a string of a guitar or tuning fork).
The frequency of mechanical resonances experienced in conventional tape drive moving head systems can be calculated from a number of factors, including mass of moving parts (head 10, spring 22, and actuator 24, for example) and a spring constant (Ks) of the spring 22. Generally speaking, conventional tape drive moving head systems are designed to place the mechanical resonance at either (1) a low frequency to keep the resonance in band and then provide other mechanisms to either eliminate or reduce effects of the resonance, or, (2) at a high frequency to push the resonance out of band, in which case no other mechanisms are required.
A method of providing a low resonance system is to utilize a high mass moving head. However, a high mass moving head causes control problems because movement of a high mass moving head is more difficult to control.
A method of providing a high resonance system is to utilize a high spring constant (Ks) for the spring 20, which increases the resonance frequency. However, a high spring constant is disadvantageous because a stiffer spring requires greater power expenditure in order to place and maintain head position (i.e., placement of the head requires continuous work against the spring).
Compared to a disk drive system (where speed of movement between tracks is critical), tape drive moving head systems do not require extremely fast track to track movements and therefore large acceleration forces are not encountered, thus making it easier to place a tape drive moving head on a selected track. However, a tape drive actuator does need to maintain a steady state in order to keep the head on the selected track.
Therefore, tape drive designers have to determine a proper mix of design elements (mass of moving parts: spring, head and actuator, and the spring constant) to determine a resulting mechanical resonance that can be reduced or eliminated effectively. Basically, the higher the mass, the lower the resonance, but more control difficulties are encountered. The higher the spring constant, the higher the resonance, but higher power is required.
Simply increasing the spring constant (Ks) higher to place the mechanical resonances out of band is not an effective solution because, in addition to higher power consumption, the higher spring constant also reduces a vertical range of motion of the moving head. Conversely, if the spring constant is too low (too loose), then the head will start floating around and control becomes more difficult.
The increasing storage capacities of modern media have added additional problems to tape drive design. These problems basically revolve around higher track densities and higher perturbation from the system because the tape is being run faster. Under normal operation, the tape being written/read moves up and down (perturbation). However, additional tracks and faster tape movement cause the up and down motion of the tape to be higher. In addition, a higher tracking bandwidth is also required because higher tape density (additional tracks, for example) requires more precise placement of the moving head. Each of these factors causes the resonance to become a main factor in the servo load of the tape deck.
An additional factor in tape drive design is damping. Damping is required to keep the spring mass system from continuing to resonate after each inflection (each up or down motion of the head, for example). The spring mass system by itself has very low damping, which causes a small inflection produces a lot of resonance. The resonance of the spring mass system eventually dies down, but normally takes a considerable amount of time. Therefore, modern tape drive designs provide damping systems to limit resonance behavior.
Damping systems typically consist of lossy materials that disrupt resonance behavior. For example, a viscous oil may be used to surround part of the spring and/or actuator to provide damping. However, because these damping systems are mechanical units, they are costly, requiring additional design, space, manufacturing steps, and maintenance.
For example, damping by lossy materials requires design decisions such as where and how to place the lossy material. Maintenance problems include leakage of the lossy material (leakage of viscous oil, for example). In addition, a tape drive system is physically limited in space, thereby limiting an amount of lossy material that may be utilized. Each of the above factors usually cause system designers to push resonance frequencies higher by stiffening the spring.
Therefore, by using a mechanical or viscous oil-type damping system, designers are still required to utilize stiffer springs, which requires a higher power system. In attempting to design with a looser spring, additional range is afforded, but at a loss of mechanical stiffness or rigidity, which is necessary in order to maintain the moving head in a vertical plane.
Accordingly, it is an object of this invention to provide a damping system for a moving head in a tape drive system that solves the above-mentioned problems and provides damping and maintains rigidity without requiring a high spring constant.
It is another object of this invention to provide a damping system for a moving head in a tape drive system that determines an amount of damping to be applied to the moving head based on a velocity of the moving head.
It is another object of the invention to provide a damping system that applies damping to a moving part electronically.
It is yet another object of the invention to provide a damping system that determines an amount of damping to be applied to a moving part based on the velocity of the moving part where the velocity is determined by more than one method.
These and other objects are accomplished by an apparatus for damping, including a first measurement device configured to measure velocity of a moving part, a damping calculation mechanism configured to determine an amount of damping based on the measured velocity, and an applicator configured to apply the damping determined to the moving part.
The first measurement device measures velocity of the moving part by any of a number of methods, including one of (1) an EMF device configured to measure a back EMF generated due to the velocity of the moving part, and (2) a signal reception device configured to receive a positioned signal corresponding to a position of the moving part, each in conjunction with a velocity calculator configured to determine the velocity of the moving part based on either the position signal received or back EMF measured.
Other methods or devices for determining the velocity of the moving part are also applicable. In one alternative embodiment, the damping system may utilize multiple velocity measurement techniques and apply the technique that provides an available or most accurate velocity at any given moment.